1. Field of the Invention
This invention relates to a composite material having an elastomer matrix which can be used as a semi-finished product in the rubber industry and, in particular, to such an elastomer composite material which is anisotropic and has a high modulus of elasticity in one direction and a great flexibility in the direction which is perpendicular thereto.
2. Description of the Prior Art
With the technical evolution of the industries in which they are used, rubber articles increasingly require advanced mechanical and thermal performance levels. It is quite apparent that such a level of performance can only be achieved by composite systems, i.e., materials whose elastomer matrix is reinforced by powder fillers, textiles or continuous or discontinuous metal elements, for example. Composite materials with elastomer matrices have for some years experienced considerable growth in all industrial fields. Such elastomer matrices, in addition to being capable of being formed into complex shapes, have beneficial characteristics at a moderate cost, as long as their mechanical properties are improved by the incorporation of a reinforcement material. Such reinforcement material may be either in the form of a mineral or organic filler (such as carbon black) or in the form of a continuous or discontinuous reinforcement manufactured from textile or metal wires (such as in tires, hoses or conveyor belts, for example).
There are numerous publications on the general subject of elastomer matrix composites. However, it should be noted that it is rather difficult to provide materials which are highly anisotropic with elastomer compound matrices by using a reinforcing material in powder form or in the form of short fibers, since mixing techniques tend to disperse the reinforcement in a homogeneous manner in the elastomer compound.
Nevertheless, elastomer matrix composites with a high modulus and high degree of anisotrophy are described in French Patent No. 2,162,691, and in French Continuation Patent No. 2,211,941 by Kleber Colombes. In the materials disclosed therein, the filler, initially in powder form, consists of high molecular weight polyethylene grains. As a result of hot homogeneous mixing between the rolls of a calender, there is an in-place fibrillation of the polyethylene grains and an alignment of the fibrils in a preferred direction. The nature of the filler, therefore, leads to a high modulus and the calendering process causes anisotropy.
Likewise, U.S. Pat. No. 4,056,591 by MONSANTO proposes the formation of anisotropic hoses made of an elastomer matrix composite reinforced with short fibers which are oriented during the composite extrusion process.
The subsequent processing of these composites for the production of manufactured articles tends--because of the necessary thermal processes--to reduce the anisotropy of the material.
On the other hand, materials with a high modulus in one direction and a high degree of anisotropy are easily provided from an elastomer matrix and a continuous reinforcement, in the form of ply, consisting of textile or metal cables. These materials are currently used, for example, in the rubber transformation industry, for the fabrication of hoses, tires, transmission belts and conveyor belts.
Nevertheless, these composites exhibit, in the directions perpendicular to that of the reinforcement, much lower mechanical properties than in the reinforcement direction which are those of the matrix, and, therefore, require the utilization of multi-layer combinations for multi-directional uses.
It should be noted that French Patents Nos. 2,162,691 and 2,211,941 were combined for prosecution purposes in the United States and resulted in U.S. Pat. No. 4,005,054. All of the above-mentioned patents are incorporated herein by reference as if the entire contents thereof were fully set forth herein.